October 31, 2014
Asteroid will get swift kick during close pass
It may sound unsettling to hear that a potential killer known as asteroid 2012 DA14 will be coming closer to Earth than telecommunication satellites on Feb. 15, but don't panic: Earth's gravitational field will give it such a kick that we'll never have to worry about it again.

"It has been getting closer to Earth for quite a while," Donald Yeomans, the head of NASA's Near Earth Object Program Office at the Jet Propulsion Laboratory, told reporters on Thursday during a preview for the close encounter. "This is the closest predicted [flyby] for this object both in the past and in the future."

NASA's calculations show that Earth's gravity will perturb the 150-foot-wide (45-meter-wide) asteroid's orbital period, which had been getting close to Earth's own one-year orbit. "Earth is going to put this one in an orbit that is considerably safer than the orbit it has been in," Yeomans said.

That makes 2012 DA14 nothing more than one of the universe's most vivid reminders that we live in a cosmic shooting gallery. The rocky asteroid's orbit is so well-known that Yeomans can say it will pass by Earth at a minimum distance of 17,200 miles (27,700 kilometers), plus or minus 100 miles. That's in the "sweet spot" between GPS satellite orbits (6,000 to 12,000 miles) and geosynchronous telecom satellites (22,000 miles), Yeomans said.

He said that there's an "extremely remote" chance that 2012 DA14 could hit a satellite on its way in or out of Earth's neighborhood, and that satellite operators were being given orbital tracking data as a precaution. But William Ailor, an expert on orbital debris at The Aerospace Corp., told NBC News that the chance is hardly worth worrying about.

"The fact is, we don't have collisions very often, even among the satellites that are there all the time," Ailor said. "Space is very active, but there's a lot of it above us."

Yeomans said the prime viewing for 2012 DA14 will be available from eastern Europe, Asia and Australia, where it will be dark during the time of closest approach at 2:24 p.m. ET Feb. 15. But even at its brightest, the asteroid will still be too dim to see with the naked eye. You'd need a binoculars or a small telescope to spot it, and you'd have to know exactly where to look from your locale. During the close approach, the asteroid will be moving across a patch of sky nearly twice as wide as the full moon every minute. "That's very fast," Yeomans said.

If you're lucky enough to catch sight of the asteroid, don't expect to see any detail. "What you would see through a small telescope would be something that looked just like a star, a small point of light," said Timothy Spahr, director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics.

Yeomans said the asteroid will be passing by at the speed of 17,500 mph (7.8 kilometers per second). "That's roughly eight times the velocity of a bullet from a high-speed rifle," he said.

Scientists aren't even sure exactly what 2012 DA14 is made of, although they suspect it's a rocky L-type asteroid. To get better information about its size and composition, experts plan to use radio telescopes at the Arecibo Observatory in Puerto Rico and at Goldstone, Calif., as well as other astronomical assets.

2012 DA14 was discovered less than a year ago by a Spanish team at the La Sagra Astronomical Observatory, and initially stirred up a wave of doomsday worries. Fortunately, NASA quickly analyzed the observations and ruled out any chance of a collision.

Experts estimate that 150-foot-wide asteroids zoom as close to Earth as 2012 DA14 will every 40 years or so, and actually hit Earth every 1,200 years.

If the asteroid were on a collision course, Feb. 15 would have been a very bad day: A rocky asteroid that big would explode into pieces on the way down, releasing as much energy as a 2.5-megaton atomic blast. Such a scenario took place in 1908 when a space rock blew up over the forests of Siberia, knocking down millions of trees over an 820-square-mile area, Yeomans said. That's not as big of a catastrophe as, say, the impact of a 6-mile-wide asteroid that killed off the dinosaurs 65 million years ago, but if Siberia's "Tunguska Event" had occurred over a city, that city would have been wiped out.

Earth may have lucked out this time, but Yeomans noted that "there are lots of asteroids we are watching where we haven't yet ruled out an Earth impact." In 2011, NASA estimated that more than 90 percent of the near-Earth objects wider than 1 kilometer (0.6 miles) have been identified and put on the tracking list. However, only about a third of the objects between a kilometer and 100 meters (330 feet) are being tracked. And NASA has detected only a small proportion of the estimated 1 million asteroids that are smaller than 100 meters but still capable of doing significant damage, asteroids like 2011 DA14.

"It's an effort that will take another decade or two," said Lindley Johnson, program executive for NASA's Near-Earth Object Observations Program. (Source: NBC News)
Story Date: February 9, 2013
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